Electronic devices use radio-frequency (RF) signals to communicate information. These radio-frequency signals enable users to talk with friends, download information, share pictures, remotely control household devices, receive global positioning information, employ radar for detection and tracking, or listen to radio stations. While radio-frequency signals can reliably carry information over long distances, extracting information directly from the radio-frequency signals and enabling the electronic device to support multiple different radio-frequency bands is challenging. To address these issues, mixers are used for frequency conversion.
As part of transmitting or receiving a signal, the mixer converts a signal from a low frequency to a high frequency or vice versa. In transmitters, the mixer upconverts a baseband signal to a radio-frequency signal. In receivers, the mixer downconverts a radio-frequency signal to a baseband signal. Through frequency conversion, the mixer enables the electronic device to process communication signals at the lower baseband frequency and also enables the same baseband frequency to be used for different radio-frequency bands.
Generally, mixers use transistors to perform the frequency conversion. One of the challenges in designing mixers involves direct current (DC) biasing of these transistors. Several factors can impact the value of a bias voltage, including variations in temperature, supply voltage, ground voltage, and input signal voltages. Without proper biasing, these transistors can increase harmonic distortion and conversion loss in the mixer, which degrades communication performance of the electronic device.